Magnetic recording medium

Abstract

A magnetic recording medium comprises a non-magnetic substrate, a thin ferromagnetic film layer overlaid on the substrate, and a polymer film formed by plasma polymerization. The thin ferromagnetic film layer is composed of ferromagnetic columnar grains. The polymer film is overlaid on the thin ferromagnetic film layer so as to permeate into the spaces between the ferromagnetic columnar grains, thereby improving the corrosion resistance and durability of the magnetic recording medium.

We claim: 
     
       1. A magnetic recording medium comprising a non-magnetic substrate, a thin ferromagnetic film layer composed of ferromagnetic columnar grains, and a polymer film formed by plasma polymerization, said polymer film being overlayed on said thin ferromagnetic film layer so as to permeate into the spaces between said ferromagnetic columnar grains, wherein said polymer film formed by plasma polymerization is prepared by polymerizing plasma of methane. 
     
     
       2. A magnetic recording medium as defined in claim 1 wherein said non-magnetic substrate is a flexible plastic film exhibiting surface roughness of 0.012 μm or less. 
     
     
       3. A magnetic recording medium as defined in claim 1 wherein said thin ferromagnetic film layer is composed of a material selected from the group consisting of cobalt, a cobalt alloy, and a cobalt alloy containing oxygen. 
     
     
       4. A magnetic recording medium as defined in claim 1 wherein said thin ferromagnetic film layer has an obliquely deposited columnar grain structure. 
     
     
       5. A magnetic recording medium as defined in claim 1 wherein said thin ferromagnetic film layer has a thickness of about 1,400 Å. 
     
     
       6. A magnetic recording medium as defined in claim 1 wherein said polymer film formed by plasma polymerization has a thickness within the range of 20 Å to 800 Å.